The goals of this project are to investigate the mechanisms by which inducible changes in the visual pigments occur and understand how these changes can be adaptive adjustments in visual sensitivity at the receptor level. The effect of light, temperature, and hormones will continue to be studied, particularly whether these environmental factors act directly on the eye, or through a centrally-mediated pathway. The changes in total amount and kind of visual pigment (prosthetic groups) are important, for the fish visual system is often used as a model for study by scientists. The neurophysiological consequences of changes (spectral sensitivity) in amount and proportions of mixtures of visual pigments will be studied before, during, and after a simulated twilight period, and related to spectral changes in light in nature. The inheritance of opsins and paired pigment systems (retinal- dehydrogenases) will be investigated in unique stocks of peociliid and goodeid fishes at The University of Michigan. A working genetic model will be prepared from pedigree studies, reciproaal crossing, biogeographic data and cytogenetics, that will serve as a basis for study of inheritance of physiological characteristics (phenotypes) of visual pigments and photoreceptors.